In general, a vacuum cleaner comprises a suction nozzle to be moved along a surface to be cleaned, and a motor for generating a suction force which is used for removing particles, typically dust and dirt particles, from the surface and displacing these particles to the inside of the vacuum cleaner. A device is arranged inside the vacuum cleaner for separating the particles from the air. As a result of a separation process, the dust can be collected in a suitable space, and clean air can be blown out.
One possibility for separating dirt particles from air is using filters for performing the separating process. Dirt particles in this context refer to particles of arbitrary size, any kind of material including both solids and liquids. Another possibility is using suitable means for creating a cyclone movement (also commonly known as vortex movement) in the sucked-in mixture of air and particles, wherein the particles are displaced towards an outside circumference of the cyclone flow under the influence of centrifugal forces, where the particles can be collected. In practical situations, the cyclone flow is created in a cyclone chamber which is shaped like a hollow cylinder having a circular interior circumference, wherein the particles are discharged from the chamber through an opening in the side wall. This opening is a dirt-duct for allowing particles to pass from the cyclone chamber towards a dirt collecting chamber. Cleaned air leaves the cyclone chamber through an air discharging pipe at the center of said cyclone chamber. Such a cyclone separating apparatus and a vacuum cleaner having the same is known from U.S. Pat. No. 7,410,535.
A commonly known problem in the field of cyclone vacuum cleaners is noise caused by the whirling air stream in the aforementioned air discharging pipe. As the air stream performs a rotational movement in the cyclone chamber about the central axis of the cylindrical cyclone chamber, the fluid maintains this rotational movement and leaves the cyclone chamber through the discharging pipe in a spiral rather than a linear stream in direction of the central axis of the air discharging pipe.
U.S. Pat. No. 6,432,154 teaches the use of a noise reducing rib formed in an air discharging pipe as a solution to the problem. The noise reducing rib is protruded on an inner wall of the air discharging pipe towards a center of the air discharging pipe and comprises a curve portion and a straight portion. This element inhibits a rotational flow about the central axis of the air discharging pipe and rather guides the air stream in the discharging pipe into a liner stream along the central axis of the air discharging pipe.